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Does Your Fuel Shine?

Posted: January 2, 2013

Probably not, but it should be polished regularly.

By: Matt Gurnsey

Many boat owners spend hours making sure their vessel shines with pride of ownership, washing, buffing and waxing their yacht to polished perfection. Little do they know that beneath that gleaming exterior in the seldom-thought-of depths of their bilge resides another oft-neglected item that also needs polishing. Of course, we’re talking about fuel.

Diesel fuel may start out clear and bright, but time spent in a boat’s tanks can create a murky fluid that can actually damage the very engines designed to burn it. Polishing the fuel restores its “shine” and helps preserve the vessel’s diesel-delivery systems.

The enemy of fuel is water, and yet the very nature of marine fuel systems almost guarantees the presence of water. A vessel’s fuel system is vented to the atmosphere, and when the tank warms up, the fuel expands, which pushes air out of the tank. As the fuel cools, it contracts, drawing air back into the tank. Water vapor in the air then condenses on the tank’s sides and becomes suspended in the fuel. Water in the tank will mix with the diesel. Some of it will remain suspended in the fuel, and the balance will settle to the bottom of the tank.

The tank can heat up a few ways. One is from the daily warming and cooling of the vessel as the ambient temperature changes over the course of the day. Another way is when unburned fuel, which has been warmed by its passage through the engine’s fuel system, is returned to the tank.

Once water is present in the tank, microbial growth starts, which eventually forms a sludge that settles to the bottom of the fuel tank with other heavy particulates. Eventually, this mixture will be drawn up the fuel pickup tubes where, in large quantities, it can overwhelm the boat’s filters.

Heavy seas will agitate the sludge at the bottom of the tank and temporarily suspend it in the fuel. Over long periods of time, even small amounts of water can damage fuel components or cause tank failure. The longer diesel is stored in the vessel, the greater the chance of water intrusion and microbial growth.

Fuel polishing is an intense filtering process to capture water, bacterial growth and particulates, which keeps diesel a clear, burnable fuel that won’t clog filters at inopportune times or damage engines.

Severe cases are usually only found after engines have shut down because of filters that are so clogged the engines are starved for fuel. Mobile services have special equipment to draw the fuel from the tank and filter it. Often, these services use expensive, heavy-duty truck-mounted equipment.

Less severe cases can be resolved by renting a portable fuel-polishing system. Usually cart mounted, these systems can be wheeled down the dock to service the vessel’s tank. Large tanks, or tanks with large amounts of sediment, may require changing the unit’s filters. One set of fresh filters is usually included as part of the rental.

A more permanent solution is to make fuel management part of your vessel’s regular maintenance routine. Onboard polishing systems facilitate the regular treatment of diesel. More than just a filter added to the engine’s fuel line, these systems operate independently and contain their own pump to allow fuel polishing at scheduled intervals. Many of these systems have a control panel with displays to indicate their status, filter replacement, vacuum pressure and timers to program the unit’s operation.

These onboard systems can be effective deterrents to future fuel problems, because they remove water, which prevents future microbial growth, and filter out existing bacteria. Usually, these onboard systems can’t solve more serious fuel-contamination issues; heavy contamination will need to be handled by the pros.

Regular cleaning can make the outside of your boat shine like new. Diesel fuel should have its own cleaning schedule to keep it in like-new condition, prevent engine damage and make it possible to get back after each trip out.